JP2014508664A5 - - Google Patents

Description

Inkjet printing method

The present invention generally relates to an inkjet printing method suitable for printing text or images on a medium.
In particular, the present invention relates to an ink jet printing method suitable for printing text or images on, for example, plastic cards such as credit cards, bank cards and the like.

  For example, a complete printing process starting with an image being displayed on the screen (original image) is printed with ink dots from an additive color primary image or RGB (red, green, blue) image. In order to obtain a corresponding subtractive primary color image or CMYK (cyan, magenta, yellow, black) image suitable for, a suitably programmed computer or microprocessor needs to perform multiple conversion steps And

The conversion step is, for example, as disclosed in patent publication WO 2009/031165 in the name of the applicant,
A calibration process in which weights are assigned to each point of the original image and a corresponding set of subtractive images is generated;
A halftone process in which subtractive color is provided to obtain an optical effect on the print medium similar to that seen on the screen;
A printing process in which CMY and optionally K dots are ejected onto a printable medium by a printhead, according to the results of a halftone process and certain printing strategies.

Printing process, in particular printing strategy (shingling Stra te di) generally, especially if you need plastic cards are printed using ink jet printing, since the drying time of the dots is very long, it is suitably programmed computer You need to prevent coalescence.

As is known, when ink dots are ejected onto a medium, there can be a coalescence problem if non-dry dots overlap each other.
The problem of coalescence is generally
-Adjacent dots overlap during printhead dot ejection, in other words this problem is defined as a carriage path (carriage path is defined as a single movement of the printhead from one edge of the media to the other. Can occur when the printhead fires overlapping dots.
-The dots ejected in the pass following the previous pass may be due to two different overlapping situations or problems where they overlap the previous dot before drying.

According to the known prior art, the problem of the first coalescence is a single grid based raster grid where each pixel (and thus the dot attached to each pixel) is assigned to various layers to prevent coalescence. is intended to be solved by the ring strategy, image here, according to the present disclosure, the layer the term, printed in a number of non-overlapping printing of a plurality of swaths or more paths (print swaths or passes) Is assumed to represent.

  For example, FIG. 1 shows a two-layer single where gray squares or dots on pixels are printed on the first layer and dots on white squares are printed on the second layer so that coalescence is prevented. Indicates a ring strategy or scheme.

In practice, the above strategy is, for example,
The assumption that each layer of dots must have a certain minimum distance, eg D _min = 84 μm,
The printer uses an asymmetrical printing resolution of 600 _vert x 1200 _horiz dots / inch (dpi), which defines a rectangular pixel with dimensions of 42 _vert x 21 _horiz μm as shown in Fig. 2a This assumption is necessary.
An eight layer shingling strategy is optimal for obtaining complete coverage since all dots are printed exactly 84 μm from each other.

In other words, an 8-layer shingling strategy is optimal to get full coverage ,
-Perfect if full coverage is not essential to reach saturation, or-Printing time is an issue and the number of layers needs to be reduced by using a lower coverage than full coverage Maybe not.

For example, assuming that 6 / 8th of full coverage may be sufficient, one can expect 6 layers to be sufficient to prevent coalescence. However, by using a prior art strategy that uses 6 layers instead of 8 layers, the required distance between dots (FIG. 2b) is not realized and the first coalescence problem appears. It is. More precisely, applicants have used eight and six shingling path respectively, together illustrates the prior art shingling strategy when printing with 600 _vert × 1200 _horiz dots / inch resolution Consider FIGS. 2a and 2b. In either case, a raster grid of pixels is represented, and the pixels are numbered according to the path to which they belong. If a dot corresponding to a pixel numbered 1 means to be printed in the first shingling pass, a pixel numbered 2 will be printed in the second pass, and so on. 600 In _vert × _{1200 horiz} dots / inch resolution, the considered pixel size is _{42 vert} × _{21 horiz μm,} also considering the fact that 6/8 of all pixels is occupied by a dot in a pseudo-random number system, the following It becomes clear.
In FIG. 2a, the prior art 8 pass shingling strategy always achieves the required coalescing distance of 84 μm.
In FIG. 2b, the 6-pass shinging strategy of the prior art only achieves a distance of 63 μm that cannot prevent coalescence.

  In summary, the applicant has generally noted that the known prior art does not optimally solve the first coalescence problem. "Optimally" means that a typical shingling strategy requires several more layers than should be given to avoid the first coalescence problem.

  Furthermore, the applicant has noted that the first coalescence problem is a problem when a plastic card needs to be printed.

  Accordingly, an object of the present invention is to provide a solution to the first coalescence problem as described above.

According to the present invention, such an object is realized by an ink jet printing method having the characteristics described in the claims below.
The present invention is a computer program product readable into the memory of at least one computer unit, software for performing the steps of the method of the present invention when the product is executed on at least one computer unit It also relates to computer program products that contain portions of code.

The claims are an integral part of the teachings of the present invention.
According to a feature of a preferred embodiment of the present invention, an ink jet printing method includes the steps of: Inserts a single ring strategy in which the printed layer is constructed.

A further feature of the present invention provides an enhancement of the general shingling process that takes into account the distance between dots composed of two or more droplets.
In accordance with another aspect of the present invention, the general shingling process is enhanced by including black dots in a set of dots and printing black dots at the same location by using C, M, Y droplets. Is brought about.

Again, further features of the present invention provide an enhancement of the general shingling process that reduces the number of layers created by the general shingling process.
These and further features and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments, given by way of non-limiting example with reference to the accompanying drawings. In the drawings, components denoted by the same or similar reference numerals indicate components having the same or similar functions and configurations.

FIG. 2 is a diagram of a prior art or typical two layer shingling based on a raster grid strategy. FIG. 6 is a diagram of an exemplary single ring strategy of 8 and 6 layers. FIG. 6 is a diagram of an exemplary single ring strategy of 8 and 6 layers. The distance evaluation map by which the distance between each dot and its adjacent dot is checked is shown. FIG. 4a shows an example of an erase mask provided by the present invention. FIG. 4b shows an example of an erase mask provided by the present invention. FIG. 4c shows an example of an erase mask provided by the present invention. FIG. 4 is a diagram illustrating an example of a black transmission coefficient that can be applied to enhance the shingling process of the present invention. FIG. 6 shows an example of a further process for enhancing the shingling process of the present invention. FIG. 6 shows an example of a further process for enhancing the shingling process of the present invention. FIG. 6 shows a statistical analysis of the results obtained by applying the shingling process according to the invention compared to an exemplary shingling method.

  Referring to FIG. 3, in order to determine whether each dot (10) and its adjacent dot (10) should be printed on the single layer, each dot (10) and its adjacent dot (10) A method is shown in which the distance between them is checked.

For example, from the actual case or the example already described, the number of shingling layers required to prevent dot coalescence by using a printing strategy based on dot distance is:
A) Minimum dot distance D _min ,
B) Number of dots and spatial distribution of dots,
According to C) print resolution (exemplary embodiment, the print resolution _is a _{600 vert} × _{1200 horiz} DPI, since the dot must take discrete locations on the medium, the print resolution, the only required Parameter)
D) Rely on the ability to optimally deliver dots between a given number of layers using an optimization process.

  Before proceeding with the disclosure of the shingling process according to the present invention, it should be emphasized that sending dots between printed layers is a typical optimization problem to be solved by a minimization method in a high dimensional space. Is important.

  Any other method must be considered as an approximation. Since the above optimization requires a huge amount of computing resources, such optimization is not discussed below.

In fact, such an approach is considered impractical.
Instead, an approximate solution is considered practical.
The present invention discloses a shingling process that uses some sort of digital sieve, briefly summarized here and generally including the following steps.

As can be readily appreciated, such steps of the shingling process are typically performed on a computer or microprocessor implemented in a printer, and in a basic embodiment includes:
Step-1: Scan all dot sets to be printed.
Step-2: For every dot in the set of all dots, delete all adjacent dots whose distance is less than D _min (the minimum distance that does not cause coalescence) and place them in the new set of dots. The current scan does not visit any more removed dots.
Step-3 At the end of the current scan , the remaining dots are assigned to the layer corresponding to the current scan ( current layer).
Step-4 Remove the dots in the current layer from the set of all dots, and Step-1 begins again for further scanning .
Step -5 of all hand dots, perform much more scan required to be assigned to a plurality of print layers corresponding to a plurality of scanning was made.

The above general process discloses a first embodiment of the present invention.
Several improvements have been introduced to enhance the general shingling process.
These improvements, alone or in combination, tend to enhance the efficiency of the general shingling process of the present invention by:
1—A pixel can be occupied by up to three droplets, thus taking into account gradually increasing the size of the dots and their minimum coalescing distance.
2- Make the shingling process more efficient by grouping the dots on the pixel.
3- If necessary, keep the print layer population in equilibrium so as to limit the print layer.

1- first enhancement As is known, when two or more droplets are deposited at the same pixel location (usually two or three droplets of different colors), usually plastic When printing on a card, the resulting dot located at the pixel location has a larger diameter than the dot produced by a single drop.

As a result, the minimum distance that does not cause coalescence must be increased accordingly.
Next, the minimum dot distance D _min is
I as the row index
And j as the column index
Symmetric distance matrix D _min = δ ₁₁ δ ₁₂ δ ₁₃
δ ₂₁ δ ₂₂ δ ₂₃
δ ₃₁ δ ₃₂ δ ₃₃
Must be replaced by
This matrix is symmetric, ie δ _ij = δ _ji
δ _ij is a necessary distance between a dot formed by i droplets and a dot formed by j droplets.

  A simple change in the general process configuration and application for generating a printed layer by using an erase mask as given in step 2 of the basic smart shingling process is the result of both interacting dots. Can explain the size.

As shown in FIGS. 4a, 4b and 4c, the structure of the erase mask varies as a function of the number of drops required for each dot of the image to be printed.
For example, to erase around the dots formed by two droplets, the erase mask of FIG. 4b must be centered on the dots of the two droplets. The erase mask is then formed by three droplets and all adjacent dots included within a distance δ ₂₃ ,
All adjacent dots formed by two or three droplets and included within a distance δ ₂₂ as well as formed by one, two or three droplets and at a distance δ ₂₁ Erase all adjacent dots that fall within the range.

A corresponding process applies to the erase mask of FIGS. 4a and 4c, respectively, applied around the dots formed by 1 and 3 droplets.
In the actual case, the applicant has a simplified distance matrix D _{min (approx)} = δ ₁₁ δ ₂₂ δ _{33 in} order to have both a limited numerical distance to be considered and a good approximation.
δ ₂₂ δ ₂₂ δ ₃₃
δ ₃₃ δ ₃₃ δ ₃₃
Noted that it is sufficient to evaluate the distance by using.

  In summary, a typical shingling process, as verified by the applicant, generally applies an approximate erase mask without departing from the process and without introducing visible errors into the printing process. It can be applied by introducing.

For example, applying the example already used to illustrate the prior art results in the approximate distance matrix containing the following values (in μm) according to the experimental measurements made by the application.
D _{min (approx)} = 84 93 105
93 93 105
105 105 105
Thus, according to a practical example, assuming that in step -2 an erasure mask needs to be applied to each dot of the set of images as a result after the halftone process, the image is
A 2D matrix whose elements are p _ij ,
The subscripts i and j give the position of the dot in the image, and the value of each element of the image as a function of the number of drops forming a dot at position (i, j),
including that p _ij = 0, p _ij = 1, p _ij = 2 or p _ij = 3.

According to the example, assuming that the resolution of the printer is 600 × 1200 dpi, the pixel size is 42 μm × 21 μm, and the erase mask is configured using the value of the distance matrix D _{min (approx)} ,
Del ¹ = a practical form of the mask in FIG. 4a
4 4 4 4 3 3 3 3 3 4 4 4 4
4 3 3 3 2 2 2 2 2 3 3 3 4
3 3 2 1 1 1 1 1 1 1 2 3 3
3 3 2 1 1 1 4 1 1 1 2 3 3
3 3 2 1 1 1 1 1 1 1 2 3 3
4 3 3 3 2 2 2 2 2 3 3 3 4
4 4 4 4 3 3 3 3 3 4 4 4 4
Del ² = a practical form of the mask in FIG.
4 4 4 4 3 3 3 3 3 4 4 4 4
4 3 3 3 1 1 1 1 1 3 3 3 4
3 3 1 1 1 1 1 1 1 1 1 3 3
3 3 1 1 1 1 4 1 1 1 1 3 3
3 3 1 1 1 1 1 1 1 1 1 3 3
4 3 3 3 1 1 1 1 1 3 3 3 4
4 4 4 4 3 3 3 3 3 4 4 4 4
Del ³ = which is a practical form of the mask in FIG.
4 4 4 4 1 1 1 1 1 4 4 4 4
4 1 1 1 1 1 1 1 1 1 1 1 4
1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 4 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1
4 1 1 1 1 1 1 1 1 1 1 1 4
4 4 4 4 1 1 1 1 1 4 4 4 4
Takes the form of
The central element of the erase mask is placed in the dot p _ij ,
-1 means the dot is unacceptable at this position;
-2 means that only one dot made of one droplet can be accepted at this position;
-3 means that only one dot made of one or two droplets can be accepted at this position;
-4 means that only one dot made up of one, two or three droplets can be accepted at this position (ie in the actual case any dot is accepted).
That is, by using a mathematical formula, when p _ij = n,
p _{i + k, j−1} ≧ Del ⁿ _{k, l}
In the case of
However, the subscripts k and l extend to the erase mask.

For example, erasure mask position (i, j) in by placing a mask Del ² centrally dot of an image to be formed by two droplets, the current layer in a position having a value of erasure mask Del ² 3 The dots that can be inserted into the dot are dots made of one or two droplets, and the dot that can be inserted into the current layer at the position where the erase mask Del ² has a value of 4, is one, two, or three This results in the dots being made of droplets.

The application of the above example corresponds to an approximate distance matrix _{Dmin (approx)} , but this can easily be extended to a more general distance matrix _Dmin .
The first enhancement provides a feature that optimizes the printing process when the halftone process is configured to give dots that contain more than one droplet.

2-Second enhancement Further enhancement of the shingling process according to the invention requires, for example, reducing the number and density of dots by giving the pixel a (convenient) dot with two or more droplets. To do.

A simple solution of this request, even if the black ink is physically not available in the printer is to make compatible the calibration process and / or halftone process to use black ink.

  This enhancement results in the logical set of inks being C M Y K, giving a formulation that replaces several C M Y triplets with one K droplet.

According to a preferred embodiment of the present invention, a known formulation called UCR (Under Color Removal) is used that operates at a color calibration level and includes the following steps.
(I) Starting from displaying the color of CMY, find the minimum of three values: U = min (C, M, Y). This value represents the gray component of the color CMY. The gray component U may be expressed using black (K) ink.
(II) As shown in FIG. 5, for example, the black transmission coefficient α = T (U) is defined as a function of U. Drawing the totality of the gray component with black ink results in a very grainy print in the light gray range, whereas dark gray benefits from the large light absorption of the K ink, so Definition is useful.
(III) Calculate new C M Y K components. However,
U = min (C, M, Y)
α = T (U)
K = α ・ U
C ′ = C−K
M ′ = M−K
Y '= YK
Here, the value α = 1 means that the wholeness of the gray component is drawn using black K ink.

  Therefore, according to the second enhancement, even when there is no black K ink available, for example, the UCR method is used to generate K dots that can be printed using three overlapping C, M, and Y droplets. Can do. The end result is that several C, M and Y dots that are potentially placed in adjacent pixels are pressed onto the same pixel.

  In other words, the data sent to the printer, including the halftone process, is prepared as if the components of the K ink were as if using a properly tuned UCR method, and then as a final step, all The K droplets are replaced by droplets superimposed by three C, M, and Y.

3-Third Enhancement The third enhancement of the shingling process according to the present invention is directed to optimizing the population of print layers in order to limit the number of print layers.

Theoretically, as shown by curve A in FIG. 6a, the shingling process according to the invention can occupy pixels in multiple layers.
Obviously, if a large number of low population layers are generated, a corresponding large number of printing passes need to be prepared.

  According to one possible enhancement of the shingling process according to the present invention, a scheme called folding is proposed here, where the folding assigns the dots assigned to the lower population layers earlier. Redistribute to a higher population.

As shown in FIG. 6b, the folding scheme gives the following steps.
_-First, the maximum number of layers L _max is constant.
_-Second , all dots assigned to the layer L _i > L _max are redistributed (folded) between L _j ≦ L _max .

According to a preferred embodiment, the dot position (i, j) does not change. For each “folded” dot, a particular layer L _j is selected according to its interaction energy E _j with the layer adjacent to that L _j .

Preferably, the energy E _j can be any decreasing monotonic function of the distance between the “folded” dot (i, j) and its neighboring dots on the layer L _j .
By applying the folding scheme as disclosed, it is possible to obtain a limited number of layers, as shown in FIG.

It should be understood that the folding scheme necessarily results in some penetration of the minimum dot distance and thus some coalescence collisions.
However, Applicants have found that the shingling process according to the present invention, which is enhanced using a folding scheme, is a better result than the known shingling process, especially when a limited number of layers are required. Proved to bring about.

In fact, Applicants have used the prior art shingling process (for example, using the 6 / 8th of the full coverage as in the prior art example, by a one-layer calculation called the pair correlation function (PCF)). Note that FIG. 7, curve A) produces PCF values. That is,
The first peak corresponding to the case where the dot pairs with itself (influx), with a distance of 0,
-For distance x <63 is exactly equal to zero, i.e. zero possibility of having a pair of dots closer than 63 μm;
-There is a first peak for the distance x = 63, i.e. it is likely to have two dots at a distance of coalescing distance _Dmin = 84 μm,
The shingling process according to the invention results in a PCF value (FIG. 7, curve B),
The first peak corresponding to the case where the dot pairs with itself (influenza), with a distance of 0,
A very small value for the pair distance x <84, ie very unlikely to have two dots at a distance closer than 84 μm,
-There is a first peak for the distance x = 84, i.e. it is likely to have two dots at a distance greater than or equal to the combined distance _Dmin = 84 [mu] m.

  In summary, applicants may find that a shingling process as disclosed with or without the aforementioned enhancements is in most cases superior to a known raster shingling process as is known. I believe there is.

  Of course, obvious changes and / or modifications to the above disclosure may be made with respect to dimensions and components, and details of the structure and method of operation described above, without departing from the scope of the invention as defined by the appended claims. It is.

Claims (8)

In the ink jet printing method comprising Ru gives a set of dots to be printed, the steps,
A first step of scanning the set of dots to be the printing,
For each dot of the set of dots, a second that erases all adjacent dots whose distance is less than at least one predetermined value (D _min ) and maintains the unerased dots as remaining dots Steps,
A third step of assigning the remaining dots to a layer corresponding to the scan ;
A fourth step of removing the remaining dots from the set of dots;
And a fifth step of re-starting or stopping the first step for further scanning when additional dots are present in the set of dots. The step of erasing all the adjacent dots comprises
Determining, for each dot in the set, a set of distance values (D _min ) for which each value is determined as a function of the number of droplets attached to the dots in the set and the adjacent dots. The ink jet printing method according to claim 1. The step of providing a set of dots comprises
3. A calibration and halftone process according to claim 1 or 2 comprising a black ink dot (K) to be printed by pressing a subtractive color (C, M, Y) drop into the same position. Inkjet printing method.   4. The calibration process includes an under color procedure (UCR) adapted to use a black transfer coefficient (α) for generating the black ink dots (K). Inkjet printing method.   The ink-jet printing method according to claim 3 or 4, wherein the halftone process is adapted to replace all black ink dots with droplets that are superimposed by three subtractive colors (C, M, Y). Defining a predetermined number of layers to be printed;
Redistributing the dots assigned to layers having a number greater than the predetermined number of layers to layers (L _j ) having a number less than or equal to the predetermined number of layers. An ink jet printing method according to claim 1. The step of redistributing the dots comprises:
The number less than the predetermined number based on an interaction function or energy function (E _j ) for the distance between the redistributed dots and the adjacent dots on the layer (L _j ) The inkjet printing method according to claim 6, comprising the step of selecting a layer (L _j ). 8. A computer program product or set of computer program products readable on the memory of at least one computer when the product is executed on at least one computer. said method comprising the portion of software code adapted to run, computer program product or computer program product set of.